Introduction:
Calcification of the mitral valve (MV) annulus and leaflets is an increasingly common cause of MV stenosis (MS).1,2Mitral annular calcification (MAC) has four principal pathophysiological mechanisms: degeneration, atherosclerosis, increased MV stress, and abnormal calcium phosphate metabolism.3 These processes lead to dystrophic calcification, increased lipid peroxidation, and chronic expression of transforming growth factor-β and inflammatory cytokines that promote phenotypic trans-differentiation of valvular interstitial cells into osteoblast-like cells.3–5 These microscopic changes can eventually cause the macroscopic changes seen with MAC, including a larger, flatter annulus with reduced mitral annular dynamism throughout the cardiac cycle.6 As the disease process continues, the dystrophic calcification extends into the left ventricular (LV) inflow tract and onto the MV leaflets, thereby obstructing LV inflow (Figure 1 ).7 This disease process has increasingly been recognized as degenerative MS (DMS)
Current guidelines for the management of patients with valvular heart disease define severe MS with a mitral valve area (MVA) ≤ 1.5 cm2 independent of the etiology of MS. According to the guidelines, severe stenosis usually corresponds to a mean transmitral pressure gradient (TMPG) of 5 to 10 mmHg at normal heart rates.8 It should be noted that these quantification values have only been validated in patients with rheumatic MS (RMS) and lack similar validation in DMS populations. The anatomic MVA of DMS can be estimated with either electrocardiogram-gated multidetector cardiac computed tomography or three-dimensional echocardiography, but their availability is limited compared to that of two-dimensional echocardiography. 6,9–11
Transthoracic echocardiography is widely available, but methods commonly used for evaluating MS severity (i.e., planimetry, pressure half-time, and color flow Doppler) have not been validated for DMS. Planimetry is challenging due to difficulty with obtaining the correct orientation of the image plane.11–13 The abnormal LV compliance that frequently accompanies DMS decreases the accuracy of the pressure-half time method and limits its applicability.10 The applicability of color flow Doppler to DMS is limited by the absence of flow contraction secondary to the MV being distorted into a tubular morphology.10,11,14 Continuity equation method is usually limited in DMS due to the frequent co-occurrence of mitral regurgitation (MR), aortic regurgitation, or atrial fibrillation in this population.6 There is ample evidence to support the TMPG as a surrogate for stenosis severity in RMS, but it is affected by changes in valve morphology and abnormal atrioventricular compliance as well as volume overload conditions such as end-stage renal disease (ESRD), and hence may not be appropriate for DMS.11,14–16
The goals of this study were to compare echocardiographic characteristics of DMS and RMS, identify echocardiographic variables reflective of DMS stenosis severity, propose a dimensionless index of MS (Dimensionless Mitral Stenosis Index, DMSI) to help with estimation of DMS severity by transthoracic echocardiography, and examine the prognostic determinants of all-cause mortality in patients with DMS.